Abstracts of Presentationsat the 1987 Annual Meeting

of The American Phytopathological SocietySouthern Division

February 1-4, 1987Nashville, TN

The American Phytopathological Society

SOUTHERN DIVISIONAnnual Meeting

February 1-4, 1987Nashville, TN

ABSTRACTS

CORRELATION OF FREQUENCY OF APHID TRANSMITTED INFECTION WITH POSSIBLE DISSEMINATION OF TELIOSPORES OF TILLETIA INDICA BYFREQUENCY OF MECHANICALLY TRANSMITTED INFECTION AND SYMPTOM TYPE IN THE PRACTICE OF BURNING WHEAT STUBBLE. M. R. Bonde, USDA-ARS,SORGHUM. J.D. Alexander and R.W. Toler, Department of Plant Pathology Frederick, MD 21701; J. M. Prescott, CIMMYT, Mexico 06600,and Microbiology, Texas A&M University, College Station 77843 D.F. Mexico; T. T. Matsumoto, CDFA, Sacramento, CA 95814; and

G. L. Peterson, USDA-ARS, Frederick, MD 21701Forty-seven sorghum accessions were planted in 6-m rows in a fieldtrial. Half of each row was mechanically inoculated with maize dwarf Tilletia indica, causal agent of Karnal bunt of wheat, hasmosaic virus strain A (MDMV-A) when the plants reached the 3-leaf been found in the Yaqui and Mayo Valleys, major wheat growingstage. The second half of each row was left for natural inoculation areas of Mexico. In the state of Sonora, Mexico, wheatvia aphids. After five weeks, disease incidence and severity were stubble is burned in the field following harvest. To deter-recorded within each treatment and accession. Regression analyses mine if T. indica teliospores were present above a burningwere run comparing levels of infection by natural inoculation with field, a Cessna 210 airplane was flown through a smoke plumelevels of infection due to mechanical inoculation and with disease at 300, 1500, and 3000 m elevations. Dustbusteli vacuumsymptom type within the same accession. With the exception of the cleaner bags were placed over air intake vents and threeaccessions with genes for "field resistance", there was a significant samples collected at each elevation. At 300 m, an average ofcorrelation (P=0.05) between aphid transmitted infection levels and 4.5 teliospores were trapped per min of flight, whereas atmechanically transmitted infection levels. In addition, the 1500 and 3000 m elevations, 3.3 and 0.5 teliospores wereaccessions with moderate to severe mosaic symptoms tended to be more trapped per min, respectively. At least 50% of the telio-easily infected through aphid transmission than those with mild spores were viable. These results suggest the possibility formosaic symptoms or those with necrotic symptoms, spread of the pathogen over long distances by air currents.

ROOT ROT OF CAMELLIA SASANQUA AND C. OLEIFERA CAUSED BY IN VIVO DICARBOXIMIDE RESISTANCE IN SCLEROTINIA MINOR FROMCYLINDROCLADIUM SP. L. W. Baxter, Jr., A. M. Sprott, S. B. PEANUT. T. B. Brenneman, Plant Pathology Dept., Univ. ofSegars, and S. G. Fagan, Department of Plant Pathology and GA, Coastal Plain Station, Tifton, GA 31793, P. M. PhippsPhysiology, Clemson University, Clemson, SC 29634-0377. and R. J. Stipes, Plant Pathology Dept., VPI & SU,

Blacksburg, VA 24061.Camellia sasanqua and C. oleifera plants are used as graftingstock for C. japonica because they are resistant to root rot One isolate of Sclerotinia minor with in vivo resistance tocaused by Phytophthora cinnamomi. During the past 2 summers dicarboximide fungicides was recovered from a field micro-many newly transplanted rooted cuttings of sasanqua & oleifera plot of peanut infested two years earlier with a fungicide-died 1 to 2 months after transplanting. Isolations from roots sensitive strain. Six total applications of iprodioneand stems of 50 diseased plants yielded a Cylindrocladium sp. (1.12 kg/ha) had been applied. Resistance was detected onInoculations confirmed this fungus as the cause. Wound inocu- medium amended with iprodione (2 uig/ml), and verified onlations on 3-yr-old plants were successful as were inoculations fungicide-treated excised peanut stems. Stem colonizationon detached, nonwounded, healthy leaves. The fungus is sup- by the resistant isolate (R-2iv) was unaffected by 40 pg/mlpressed completely in culture by benomyl at 10 pg/ ml but is of iprodione, a concentration lethal to sensitive isolatesnot killed. Fungal transplants left for 2 wk on carrot juice as well as those with previously induced in vitro resis-agar (CJA) amended with benomyl (1200 pg/ml) grew when placed tance. R-2iv was highly resistant to dicloran and vin-on CJA. Captan, triadimefon, PCNB, glycophene, etridiazol, and clozolin which also have good activity against S. minor.chlorothalonil did not give effective control. Scraped 4- to Although in vitro dicarboximide resistance occurs readily5-day-old colonies of Cylindrocladium formed abundant conidia, in S. minor, this is the first report of field resistance.and after 7-10 days more it formed fertile perithecia.

SPATIAL PATTERN OF MACROPHOMINA PHASEOLINA IN TEN FIELDS INPHENOL-OXIDIZING ISOZYME EXPRESSION IN WATERMELON NORTH CAROLINA. C. Lee Campbell, Department of PlantINDUCED BY DIFFERENT RACES OF FUSARIUM OXYSPORUM Pathology, North Carolina State University, Raleigh 27695.F.SP. NIVEUM. C. L. Biles and R. D. Martyn, Department of PlantPathology and Microbiology, Texas A&M University, College Station, Propagules of Macrophomina phaseolina are usually aggregated in77843. field soils. To quantify propagule aggregation and to

ascertain whether soil texture influences spatial pattern of M.Watermelons were protected from a virulent race of Fusarium phaseolina, a total of 10 fields were studied. In each fieldoxysporum f.sp. niveum when previously inoculated (induced) with an one core sample (2.5X10-12 cm) was removed from each of 150avirulent race. Horizontal IEF-PAGE was used to examine differences 6.1X6.1 m contiguous quadrats and a 10 g subsample of soil wasin three phenol-oxidizing enzymes [peroxidase (PER), polyphenol- assayed for M. phaseolina. Mean inoculum density (ID) rangedoxidase (PPO), and shikimate dehydrogenase (SDH)] in compatible, from 3.3-77.-anTd 11.8-42.2 propagules per 10 g soil innoncompatible, and induced-resistant reactions. Isozyme patterns Edgecombe and Wayne County fields, respectively. Values ofdiffered with the tissue examined (root, stem, leaves). The PER loci Morisita's index ranged from 1.17-3.09 indicating low toapparently recognized the avirulent race 12 hr after induction but did moderate aggregation of propagules. Soil surface texture,not recognize the virulent one. PPO loci responded similarly to both determined for ten 15-quadrat blocks in each field, wasthe virulent and avirulent races. Additional PPO isozymes were generally silt loam, loamy sand, or sand. Mean ID of the 15-expressed in the induced treatments 24 hr after challenge with the quadrat blocks of M. phaseolina was not generally correlatedvirulent race but not in the compatible treatments. SDH isozyme significantly with percentage sand, silt, or clay. Thus otherpatterns were similar at each time in the compatible, noncompatible, factors must account for propagule aggregation of M. phaseolinaand induced-resistant reactions, within the fields examined.

Camera-ready abstracts are published as they were submitted by the Protomyces gravidus as a potential mycoherbicide of giantDivision. The abstracts are not edited or typed in the APS ragweed, Ambrosia trifida. R. D. Cartwright and G. E.headquarters offices. Templeton, Department of Plant Pathology, University of

Vol. 77, No. 4, 1987 639

Arkansas, Fayetteville, AR 72701. of Horticulture and L.A., Oklahoma State University,Stillwater, OK 74078-0285.

An indigenous fungal pathogen, Protomyces gravidus, is beingconsidered for biological control of giant ragweed. It causes Control of Cercospora asparagi on asparagus was compared bylarge stem galls permeated with mycelium and resting spores. burning or soil incorporation of fern residue, and a

Pure cultures were isolated by germination of overwintered fungicide. Ferns were mowed (March) and left as residue on

resting spores. On solid media or in liquid culture, it grew surface of 16 blocks of asparagus. Residue was roto-tilledas a yeast at constant temperature between 12-28C, o~timum at into soil in 4 blocks and burned in 4 blocks prior to spear20C. Seedlings were sprayed with washed cells (ixl 0) of P. production in April. Spears were allowed to grow aftergravidus in the greenhouse. Maximum infection occurred after harvest to produce ferns. Chlorothalonil (1.75 kg (a.i.)/ha)incubation at 20C and 48 hrs 100% RH. Stem and leaf galls was applied to ferns of 4 blocks on 9, 24 July and 12 August.

were produced 2-4 weeks after inoculation. A number of Untreated blocks were controls. Disease severity was assessedseedlings (2 leaf stage) were killed, but older seedlings (4-6 weekly (July-October). Area under disease progress curveleaf stage) developed non-lethal infections. Only giant and values were significantly less (P=0.01) on ferns in fungicidecommon ragweed, Ambrosia artemisiifolia, were susceptible in protected blocks compared to other treatments. Burning the

host range studies. Low virulence is a major factor limiting residue also significantly reduced disease (P=O.05) compared

potential of P. gravidus as a mycoherbicide. to soil incorporation of residue and controls.

Effect of fertilizer level and cultivar on susceptibility of RESISTANCE TO PEANUT STRIPE VIRUS IN ARACHIS GERM PLASM.

Calatheas to Bip01aris setariae. A. R. Chase, University of J. N. Culver, J. L. Sherwood, and H. A. MeloukI, DepartmentFlorida, IFAS, Agricultural Research and Education Center, of Plant Pathology, Oklahoma State University and USDA-ARS

1,

Apopka, FL 32703. Stillwater, OK 74078-0285.

Calathea species and cultivars were grown for 2 mo in a steamtreated potting medium top-dressed with Osmocote 19:6:12 at one Peanut accessions of the Arachis section7 A. diogoi (PT

of the following rates: 2, 5, 8, 11, 14, and 17 g/15-cm pot. 468141 and PI 468142), A. helodes (PI 468144), Arachis Ek.The recommended rate is approximately 4 g/15-cm every 3 mo. (P1468345 and PI 468169), and of the Rhizomatosae sectionPlants were then inoculated with a conidial suspension (1 x 10 (PI 468174, PI 468363, and PI 468366), were evaluated forconidia/ml) of Bipolaris setariae and placed in plastic bags resistance to peanut stripe virus (PStV). These entriesfor 3 days. Plants received intermittent misting (5 sec/30 min, and a susceptible cultivar Argentine were mechanically

12 hr/day) starting 24 hr before inoculation and continuing inoculated with PStV. Three to 4 weeks after inoculation,until test completion. Rate of fertilizer affected plant leaves from each entry were tested for PStV infection.

quality, number of leaves, height, and leachate soluble salts Infection was determined by symptomatology, local-lesionbut did not affect susceptibility to the pathogen. Calathea assay on Chenopodium amaranticolor, enzyme-linked

argentea 'Silver Portrait' and 'Vandenheckei' were most immunosorbant assay, and electron microscopy. All entries

susceptible with C. insignis also susceptible. Calathea except for PI 468169 and the susceptible cultivar Argentine

makoyana was moderately resistant and C. louisae and C. roseo- were negative for virus infection. To our knowledge, this

picta were highly resistant. is the first report of resistance to PStV in Arachis.

Effect of fertilizer rate on susceptibility of Ficus lyrata to FORMATION OF HYBRID CITRUS RINGSPOT VIRUS ISOLATES BYPseudomonas cichorri. A. R. Chase, University of Florida, IFAS, COMPONENT MIXING. J. V. da Graca and R. F. Lee, University

Agricultural Research and Education Center, Apopka, FL 32703. of Florida, CREC, Lake Alfred 33850.The effect of fertilizer rate on severity of Pseudomonas leaf The top and bottom components of two isolates of citrusspot of Ficus lyrata was tested using a strain of P. cichorii ringspot virus (CRSV), one causing bark lesions (68), theisolated from that plant. Plants were grown in a Canadian peat other not (4E), were separated by sucrose density gradientand pine bark mix (50-50) top-dressed with various rates of centrifugation. The top component of each was mixed withOsmocote 19:6:12 for 2 mo prior to inoculation. The rates were the bottom component of the other and inoculated onto1, 4, 7, 10, 13, and 16 g/12.5-cm pot; 4 g/12.5-cm pot is the Chenopodium quinoa, a local lesion host which reactsrecommended rate. Plants were misted (5 sec/30 min, 12 hr/day) differently to 4E and 6B1 in terms of lesion appearance and

starting 24 hr prior to inoculation and continuing until test number. The 4E bottom component enhanced the infectivity ofcompletion. Plants were sprayed with a bacterial suspension (1 x the 6B1 top component to give lesion counts intermediate100 cfu/ml in 0.01 M MgS0 4 ) and placed in plastic bags for 3 between the two type isolates, while the reverse combinationdays. Height, number of leaves, and foliage quality were did not significantly alter lesion formation. Singleaffected quadratically by fertilizer rate with optimal values at lesions of the two hybrid CRSV isolates were inoculated ontorates between 4 and 13 g/pot. The mean percentage of foliage C. quinoa, and then back to citrus to determine if eitherarea with symptoms was least at the 1 g/pot rate and highest at retains the ability to form bark lesions. Results of thisthe 4 g/pot rate. At rates above 4 g/pot, a linear decrease in are not yet available.disease severity occurred as fertilizer rate increased. Thistest was performed twice between June and September, 1986.

SPREAD OF DIAPORTHE PHASEOLORUM VAR. CAULIVORA IN A SOYBEANFIELD FROM AN INOCULUM POINT SOURCE. J.P. Damicone, G.T.

POWDERY MILDEW RESISTANCE AMONG NATIVE POPULATIONS OF CEDAR ELM. Berggren, and J.P. Snow, Dept. of Plant Pathology & CropP. F. Colbaugh, S. L. Fields, and B. J. Simpson. Texas Agri- Physiology, Louisiana State University, Baton Rouge, LA 70803.cultural Experiment Station, Texas A&M University Research andExtension Center, Dallas, Texas 75252 Oat kernels colonized by mycelium of Diaporthe phaseolorum2 var.

caulivora (DPC) were placed in the center quadrate (.75 m ) of

Cedar elm (Ulmus crassifolia Nutt.) is widely used as a land- plots planted with Wilstar 550 or Deltapine 105 soybean culti-scape tree TIn North Central Texas. Nurserymen obtain their vars. Ascospores and conidia were produced in perithecia andtrees from native stands that grow along streams or on dry pycnidia, respectively, formed on the kernels in the field. Thelimestone hills. While the tree is valued for its beauty and number of lesions and/or cankers per plant, proportion ofadaptation to local growing conditions, susceptibility to pow- plants infected, and proportion of plants dead were quantifieddery mildew is a common problem. Field investigations over a on 4 dates beginning at the RI stage and yield was measured in2-year period determined the severity of powdery mildew on cedar quadrates radiating from the inoculum. Cultivar had no effectelm trees on Dallas area landscapes. Observations of 247 trees on disease measures and disease progress curves for each wereduring October, 1986, indicated 237 trees had slight to severe monocyclic. Disease measures on both cultivars and yield losssymptoms of the disease while 10 trees showed no visible symp- of Wilstar 550 declined significantly with distance fromtoms. Variations in seed production were also noted among the inoculum. Although symptomatic plants were detected up to 4.5 mtree population. Of trees observed during the fall seeding from the inoculum, incidence was low past 1.5 m. Environmentalseason, 42% produced moderate or abundant seed while 58% variables in relation to DPC spread will be discussed.produced low levels of seed. These observations indicateselections of cedar elm can be used to overcome problems ofpowdery mildew susceptibility and heavy seed production. A SEARCH FOR COMMON GENE PRODUCTS AMONG FLUORESCENT

PSEUDOMONAS AND BACILLUS SPECIES ANTAGONISTIC TO SEPTORIA

TRITICI. H. M. El-Nashaar and F. J. Gough. USDA-ARS, P.O.

COMPARISON OF CULTURAL AND FUNGICIDAL CONTROLS FOR CERCOSPORA Box 1029, Stillwater, OK 74078-0285

BLIGHT OF ASPARAGUS. K. E. ConwayI, J. E. Motes2

, B. Bostian2

and C. J. Foor1

, Department of Plant Pathology1

and Department Soluble proteins from two cultures of Pseudomonas fluorescens

640 PHYTOPATHOLOGY

and one culture each of Bacillus subtlis and B. pumilus were ered a significant pathogen on muscadine (Vitis rotundifolia),compared using tube cell polyacrylamide gel electrophoresis. though AT biovar 3 is common and serious on V. vinifera andOne P. fluorescens isolate was obtained from Texas (C. other Vitis spp. In a recent planting of muscadines, a seriousHowell), the remaining cultures were from Oklahoma (F. incidence of apparent crown gall was found on Georgia 15-5-3Mehdizadegan). Each culture suppressed in vitro growth of and Georgia 23-45 selections. Similar occurrences have sinceSeptoria tritici (=Mycosphaerella graminicola) and development been noted on Doreen, Magnolia, Sugargate, Carlos, and otherof Septoria triciti blotch. Bacterial cells were cultivars. Galls were usually located near the soil line, andultrasonically disrupted and centrifuged at 45,000 g for 30 occasionally on aerial portions of plants. When severe, aerialmin. The supernatant was used as the soluble protein portions died. Agrobacterium spp. were isolated from both V.fractions. Although the four cultures differed in quantity rotundifolia, and V. vinifera galls, and pathogenicity indi-and quality of their protein, protein banding at Rf values of cated. Extensive sampling of symptomless muscadine cultivars0.05, 0.21, and 0.65 was common for all isolates. These from several vineyards (where vascular juices were extractedcommon proteins may be involved in antibiosis of S. tritici; and plated on RS and NKS media) suggested a high percentage ofbut further investigation is required. cultivated muscadines infested with Agrobacterium spp.

COMMON GENE PRODUCTS AMONG PSEUDOMONAS AND ACINETOBACTER COMPARISON OF VIRULENCE OF TOMATO AND PEPPER ISOLATES OF

ISOLATES ANTAGONISTIC TO GAEUMANNOMYCES GRAMINIS VAR. TRITICI. COLLETOTRICHUM SPP. J. F. Hadden and L. L. Black, Dept.E. N. Ei-NashaarI, E. E. Wagih, and F. J. GoughI. USD-A-AS of Plant Path. and Crop Physiol., La. Agric. Expt. Sta.,Plant Science and Water Conservation Lab., P.O. Box 1029, La. State Univ. Agric. Ctr., Baton Rouge, LA 70803Stillwater, OK 74078-0285F and Plant Pathology Dept., Detached fruit of pepper (cayenne and Yolo Wonder) and tomato

(Heinz 1350 and Roma F021) were inoculated with twenty-twoSoluble protein fractions from one nonfluorescent and six isolates of Colletotrichum from pepper and tomato representingfluorescent Pseudomonads and an Acinetobacter sp., that were C. acutatum, C. capsici, C coccodes, and C. gloeosporioides.Fruit were wound inoculated with a spore suspension of 10'suppressive to take-all disease of wheat (caused by spores/ml using a hypodermic syringe and held at roomGaeumannomyces graminis var. tritici, Ggt) and which inhibited temperature. Percent fruit showing lesion development andgrowth of Ggt in vitro, were compared using native lesion diameter were recorded after 9 days. Only 43% ofdisc-polyacrylamide gel electrophoresis. Ultrasonically C. gloeosporioides-inoculated fruit showed lesion developmentdisrupted cells were centrifuged at 45,000 g for 30 min. compared to 87%, 74%, and 75%, for C. acutatum, C. capsici,Soluble protein fractions in the supernatant separated on 10% and C. coccodes, respectively. Average lesion diameterpolyacrylamide gel revealed both qualitative and quantitative caused by each species was similar (C. gloeosporioides,differences. Proteins banding at Rf values of 0.02, 0.05, 18.7mm; C. acutatum, 24.6mm; C. capsici, 21mm; and C.0.07, 0.19, 0.21, 0.45, and 0.57 were common among the eight coccodes, 21nm).isolates. The possible involvement of one or more of theseproteins in the antagonistic mechanism is being investigated.

XYLEM-LIMITED BACTERIA CAUSE BLIGHT SYMPTOMS IN CITRUS.

A VIRUS DISEASE OF SORGHUM x SUDANGRASS HYBRID IN TEXAS. D. L. Hopkins, Agricultural Research and Education Center,L.M. Giorda, R.W. Toler, and G. Odvody. Dept. of Plant Path. and IFAS, University of Florida, Leesburg, FL 32749-0388Microbiol., Tx. Agr. Exp. Sta., College Station, TX 77843. Xylem-limited, Gram-negative bacteria (XLB) isolated from

various hosts ware used to inoculate seedlings of rough lemon,Disease symptoms developed 20-25 days after virus inoculation of the citrus rootstock that is most susceptible to blight.'Sudax' (sorghum x sudangrass hybrid) from field infected plants. After 2 years, stunt and dieback symptoms were observed inSymptoms included yellow streaks and bands in half of the leaf, seedlings inoculated with XLB isolates from grapevine, peach,followed by chlorosis, necrosis, and death of the plant. seedlackberryuand with XLB isolates om theIsometric particles, 22-26 nm in diameter, were observed in oak, blackberry, and goldenrod. Three isolates of theembedded tissue of sorghum 'Sudax' and sweet corn 'Silver Queen'. XLB obtained from citrus with blight were used to inoculateThe virus was not transmitted by Schizaphis graminum or rough lemon, rangpur lime, and sweet orange citrus seedlings.Rhopalosiphum maidis but was mechanically transmitted to 2-10% of One citrus XLB isolate produced stunt and dieback symptoms ininoculated 'Sudax'. Twenty two species and cultivars of mono- and all three rootstocks, with more severe symptoms occurring indicotyledonous plants were inoculated with the virus. Symptoms rough lemon. These inoculated seedlings also had reducedappeared only in sweet corn, sorghum, and in the commercial jumbo r con .u these inos tem set ins a levad zincedItalan ushbea (N). lthughsimiar somtri patices orewater conductivity in stem sections and elevated zinc levelsItalian bush bean (NK). Although similar isometric particles were in trunk wood and phloem, which are diagnostic tests forobserved in bean, the virus was not recovered when back-inoculated blight. Three sweet orange trees on rough lemon rootstockto 'Sudax'. Infected sap from sorghum and corn were tested inoculated with XLB also developed symptoms.against PMV, SAD, BrMV, CMV, MCMV antisera with negative results.

INDUCTION OF SYNCHRONIZED ASEXUAL DEVELOPMENT OF ASPERGILLUSREFRACTIVE QUALITY OF BACTERIAL COLONIES AS A MEANS TO PARASITICUS IN LIQUID CULTURE. S. T. Kendall and D. M.DIFFERENTIATE XANTHOMONAS CAMPESTRIS PV. PRUNI FROM OTHER Wilson, Department of Plant Pathology, University of Georgia,YELLOW-PIGMENTED BACTERIA. R. Gitaitis, J. Hamm, and P. Coastal Plain Experiment Station, Tifton, GA 31793.Bertrand. Department of Plant Pathology, Coastal PlainExperiment Station, University of Georgia, Tifton, GA 31793. A temperature mediated shake culture method was developed

which synchronized conidial production in A. parasiticusPopulations of Xanthomonas campestris pv. pruni (XPR) were (NRRL 2999). Glass culture tubes (150 x 24 mm) containingmonitored on peach leaves by spreading 0.1 ml samples from five ml of a defined liquid medium (pH 4.5) were prewarmed toleaf washings on to the surface of nutrient agar plates. 41C and inoculated with a washed conidial suspensionColonies were counted after incubation at 30C for 48-72 hr. (5 x 10 ___f___ -T u w(x 0conidia/ml) of A. parasiticus. The tubes wereIdentifications were based on the patterns in individual incubated for 20 hr at 41C followed by 28 hr at 30C. Duringcolonies when plates were held 15 cm above a clear templet the 41C incubation floating conidia swelled two times theirthat contained horizontal black lines spaced 3 mm apart. The original size, germinated, and formed a loose mat. Continuedtemplet was placed on the translucent surface of a light-box incubation at 30C resulted in synchronized asexual develop-that was subilluminated with two 45.7 cm white fluorescent ment and by 10 hr at 30C conidiogenesis was observed. Rapidlamps (20 Joules/sec). The clarity of XPR colonies created an spore production followed which leveled off after about 20 hrundistorted view of discrete straight lines when the templet as determined by spore counts. Aflatoxin synthesis occurredwas viewed through the colony. Most other yellow colonies in this system at 30C. Addition of beta-ionone to culturescontained various distorted patterns or were opaque. Initial resulted in altered aflatoxin synthesis and atypical conidialidentifications made by using the straight-line templet development.exceeded 98 percent accuracy.

REDUCTION OF LESIONS CAUSED BY RHIZOCTONIA SP. ON STEMSOCCURRENCE OF CROWN GALL ON MUSCADINE GRAPES. C.H.Graves,Jr., OF JUVENILE SOYBEAN AND BELAN FLA IS WITH AR.P. Vine and C.P. Hegwood,Jr. Depts. of Plant Path. and Weed PREEMERGENT SPRAY OF SN 84364 (FLUTONANIL) ON THE SOIL.Sci., Food Sci. and Human Nutri., Miss. State, MS 39762, and T. A. Kucharek and R. E. Cullen. Plant Pathology Dept., University ofTruck Crops Branch Expt. Sta., Crystal Springs, MS 39059. Florida, Gainesville, 32611.

Agrobacterium tumefaciens (AT) has not been generally consid- In separate field tests on soybeans and beans, a preemergent, banded

Vol. 77, No. 4, 1987 641

(.25-.31m) spray on the soil along the row center with SN 84364 (50WP chlorothalonil/ha. Pod yields were increased and leafspotat 1.12 kg/ha) reduced the number of lesions caused by Rhizoctonia sp. diseases were reduced in all fungicide treated plots.on stems by 49 and. 63%, respectively. The addition of metalaxyl ( EC There was an estimated 675 kg/ha increase in pod yields inat 1.2 I/ha) to the spray further reduced lesions on soybeans but not on two versus three (approximately $480 increase in return perbeans. In two additional field tests on soybeans where SN 84364 was ha). Residue was significantly greater from ground spraytank mixed with metalaxyl, lesions were reduced by 47 and 24% and the application. These results tend to explain the increase in

metalaxyl by itself reduced lesions by 34% in the former test but not peanut yield when fungicides are applied in the irrigationthe other. Spray volume was 187 and 74 I/ha for the bean anq soybean water.

tests, respectively, but spray pressure was identical (2.lkg/cm ).

CERCOSPORIN PRODUCTION AND PATHOGENICITY OF CERCOSPORA

ANALYSIS OF LATE LEAF SPOT (CERCOSPORIDIUM PEBSONATUM) ARACHIDICOLA ISOLATES. H. A. Melouk and W. Schuh. USDA-ARS,DISEASE COMPONENTS TO EXPLAIN THE RATE-REDUCING EFFECTS OF A Plant Pathology Dept., Oklahoma State University, Stillwater,PROTECTANT AND A STEROL INHIBITING FUNGICIDE. J. Labrinos, OK 74078-0285.F.W. Nutter, Jr., and S.C. Alderman, Dept. Plant Pathology,University of Georgia, Athens 30602. Four isolates of C. arachidicola (CA) obtained from diseased

peanut grown in Oklahoma were maintained on peanut-oatmealAnalysis of disease components can be used to explain how agar (POA). Two isolates were classified as "Pink" becausefungicides reduce the infection rate 'r'. To differentially cercosporin was detected in POA by thin layer chromatography,reduce the rate of infection, HWG 1608 (sterol inhibitor) and two were classified as "Black" because cercosporin was notand chlorothalonil (protectant) fungicides were applied at detected. Differences in parasitic fitness parametersdifferent levels of active ingredient (a.i.) to field plots (lesions/leaf, necrotic area/leaf, conidia/mm

2 necrotic area,

of peanut (Arachis hypogea 'Florunner'). Sprays were and percent necrotic area) were found between isolates on theinitiated when Cercosporidium personatum reached the 1% level cv. Tamnut 74. However, no relation between cercosporinof infection. Although both fungicides reduced 'r' as a.i. production and the parasitic fitness parameters was observed.was increased, HWG 1608 reduced 'r' to a much greater extent Thus, cercosporin production does not appear to be a factor inthan chlorothalonil. Analysis of disease components showed determining the pathogenicity of the "Black" and "Pink"that reduction in 'r' was largely attributed to fungicidal isolates of CA.effects on sporulation and lesion number. The regressioncoefficient relating a.i. to the log of number of sporesproduced per lesion was -0.474 for HWG 1608 and -0.213 forchlorothalonil. The level of a.i. did not affect lesion size. INHERITANCE OF RESISTANCE TO VIRUSES IN COWPEAS. A. Melton,

W. L. Ogle, 0. W. Barnett, and J. D. Caldwell. Department ofHorticulture, Clemson University, Clemson, SC 29634.

BIOLOGICAL CONTROL OF RHIZOCTONIA SOLANI ON COTTON BY Vigna unguiculata subsp. unguiculata populations wereLAETISARIA ARVALIS AND A MYCOPHAGOUS INSECT, PROISOTOMA MINUTA. inoculated with southern bean mosaic virus-cowpea strainRobert Lartey, E. A. Curl, and Curt M. Peterson, Dept. of Plant (SBMV-C), blackeye cowpea mosaic virus (BlCMV), cowpea severePathology, and Dept. of Botany and Microbiology, Auburn mosaic virus (CSMV) and cowpea chlorotic mottle virus (CCMV).University, AL 36849. Populations were Mississippi Silver (MS) and California #5

Blackeye, their F1 , and reciprocal F1 , backcross to eachBiological control of Rhizoctonia solani on seedling cotton by parent and F2 progenies. Sensitive or tolerant planta fungal agent, Laetisaria arvalis, and a mycophagous micro- responses were rated by symptom expression. Resistant orarthropod, Proisotoma minuta (Insecta: Collembola), was susceptible plant responses were rated by detection of virusassessed in sterilized and non-sterilized soil infested with with enzyme-linked immunosorbent assay (ELISA). Two pairs ofRhizoctonia inoculum densities of 0.01 to 0.15 g/kg soil. L. recessive genes (sbc-l and sbc-2) controlled resistance toarvalis applied to the seed reduced disease severity more SBMV-C movement in MS. Tolerance to SBMV-C in MS waseffectively than when applied to the soil; in sterilized soil controlled by two recessive genes. One recessive gene pair inthis fungus alone caused minor root injury. Collembola at MS controlled resistance to infection by B1CMV. MS and all1000/kg soil suppressed disease without causing root injury, subsequent generations having MS as a parent were infected byThe two agents were compatible and, when applied together, the CSMV but were rated as tolerant due to reduced symptomdisease control benefit was significantly greater than for severity. MS contained no resistance or tolerance to CCMV.either used alone. Seedling emergence and root and shoot dryweights also varied according to the single agent or combina-tion used. Overall, P. minuta was the more effective of thetwo agents. A ROT OF ONION BULBS CAUSED BY GEOTRICHUM SP. M. E.

Miller, Texas Agricultural Experiment Station, T. H.Camp, USDA-ARS, Weslaco, TX 78596, R. A. Taber, andL. M. Pike, Texas A&M University, College Station,

EFFECTS OF POWDERY MILDEW, TRIADIMENOL SEED TREATMENTS, AND TX 77843.TRIADEMEFON FOLIAR SPRAYS ON YIELD OF WINTER WHEAT IN NORTHCAROLINA. S. Leath, USDA-ARS, Department of Plant Pathology, An undescribed bulb rot caused by Geotrichum sp.North Carolina State University, Raleigh, NC 27695-7616. was found on Texas Grano 1015Y (TG 1015Y) onions

in south Texas in 1986. TG 1015Y bylbs inoculatedWheat plots were established in central and eastern North with 0.5 ml of a 30,000 conidia ml aqueous sus-Carolina in the fall of 1985 to determine yield reduction pension of the fungus developed small, watery,caused by Erysiphe graminis f. sp. tritici on wheat varieties translucent lesions after 3 days incubation at 20C.Saluda and Coker 983. The efficacy or triadimenol applied as a Lesions increased to 4-6 cm after 7 days. Differ-seed treatment with and without different triadimefon foliar ences in disease severity occurred among 12 onionspray schedules also wasevaluated for the control of powdery lines. TG 1015Y and 91438 had significantly highermildew. Plots at both locations were 2.4 m

2, bordered by 1.2 m (P = 0.05) disease severity ratings while TG 1030Y

of barley and arranged in a randomized complete block design and 91486 had significantly lower ratings than thewith five replications. Yields for Saluda in the untreated other lines. There was a linear relationship (Y =plots were 79% of the full controls, whereas yields in plots -2.25 + 0.23X, R = 0.8) between disease severitytreated with triadimenol were 89% of the full controls, and temperature from 10-30C.Treatment differences (k--0.05) for mildew severity wereobserved in both Saluda and the resistant variety, Coker 983.No clear differences existed for test weight or kernel weight.Seed treatment may provide acceptable and economical control of THE EFFECTS OF RING NEMATODE, CRICONEMELLA ORNATA, ON THEpowdery mildew in certain circumstances. NUTRIENT CONTENT OF CENTIPEDEGRASS. M. R. NEWNAM AND L. T.

LUCAS, PLANT PATHOLOGY DEPARTMENT, NORTH CAROLINA STATEUNIVERSITY, RALEIGH, NC 27695-7616.

INFLUENCE OF CHLOROTHALONIL APPLIED IN IRRIGATION WATER ON Changes in nutrient content were detected in centipedegrassYIELD AND FOLIAGE RESIDUE. Robert H. Littrell. that was grown in soil infested with different initial

population (P.) levels of Criconemella ornata. Nitrogen,A quandrant in .4 ha center-pivot system was used to potassium, anb iron content decreased, w s, phosphorus,establish four-row plots 4.3 x 9.1 m to apply calcium, manganese and zinc levels increased in the shootchlorothalonil with (1) conventional ground sprayer, (2) tissue of parasitized plants. Nitrogen, potassium, sulfur,irrigation water (no traffic), and (3) irrigation water iron, manganese, and zinc content decreased, whereas,(with traffic). Fungicide was applied seven times in 4 mm phosphorus, calcium, magnesium, and copper levels increased inof water or 96 X of spray per ha using 1.24 kg a.i. the nematode-parasitized roots. Significant negative

642 PHYTOPATHOLOGY

correlations were obtained in the shoot tissue analysis between day 105. Total dry matter production was not significantlyPi and nitrogen, potassium, iron and molybenum in the shoots, different between line 64 and 'Yuchi'; however, overall sur-and between shoot nitrogen and phosphorus, iron and molybenum vival rate of inoculated plants was 94% for line 64 compared toin the shoots. These changes in nutrient levels may result in 55% for 'Yuchi'. Age of plants at inoculation significantlyplants having lower levels of stress tolerance to drought and affected total dry matter production (P=.01), with greatestcold weather. reductions occurring the earlier the plant was inoculated.

Current work is underway to identify other such 'tolerant'lines and evaluate their progeny for virus resistance.

DETECTION OF PLANT DISEASE GRADIENTS USING A HAND-HELD,MULTISPECTRAL RADIOMETER. F. W. Nutter, Jr., Department ofPlant Pathology, University of Georgia, Athens 30602. SCREENING FOR RESISTANCE TO PHYTOPHTHORA ROOT ROT IN CRIMSON

CLOVER. R. G. Pratt and W. E. Knight, USDA, ARS, ForageA multispectral radiometer was used to determine if plant Research Unit, P.O. Box 5367, Mississippi State, MS 39762disease gradients could be detected by measuring the amountand quality of sunlight reflected from peanut (Arachis Cultivars and inbred lines of crimson clover (Trifolium incar-hypogaea) canopies. Reflectance measurements (500 to 50 nm natum L.) were screened for resistance to root rot caused by awavelength range) and visual assessments of disease severity PhVtophthora sp. in greenhouse tests for 5 years. Potentiallywere taken within and across plant rows at various distances resistant plants from cultivars were selfed, and their progenyfrom peanut rust (Puccinia arachidis) or late leafspot were further screened and selfed for up to four additional(Cercosporidium personatum) disease foci. Reflectance measure- generations. Inbred lines were compared with parental culti-ments and visual assessments were highly correlated for all vars and with each other on the basis of scores for severitygradients measured. Reflectance in the 800 nm wavelength of root disease symptoms and mortality. Five of 18 S lines,band increased and visual disease severity decreased, with and 7 of 18 S lines, manifested significant resistance in aincreasing distance from disease foci. Although disease final severe Lest. Segregation for resistance within Sgradients were detected with either method, the reflectance through S4 generations was suggested by differences in Aiseasemethod provided data twenty times faster. The development of scores of related S2 to S5 lines. Results suggest that highmodels to describe disease gradients, based upon reflectance levels of resistance to P ytophthora root rot may not be pre-data, may provide a standardized and objective method to sent within cultivars of crimson clover. However, moderatedetect and quantify plant disease gradients in other crops. levels of resistance can be obtained that enable plants to

survive under prolonged conditions favorable for disease.

THE NATURE OF ICE NUCLEATION-ACTIVE BACTERIA ASSOCIATED WITHAPPLE AND PEACH TREES IN GEORGIA AND INFLUENCE OF VARIOUS Greenhouse Evaluation of Fungicides for Control ofCHEMICALS ON THEIR ICE NUCLEATION ACTIVITY. J. W. Olive and Strawberry Anthracnose-Crown Rot. Barbara J. Smith,S. M. McCarter, Dept. Plant Pathology, University of Georgia, USDA-ARS Small Fruit Research Station Poplarville, MS 39470

Athens, GA 30602. Three fungicides were tested on 4 strawberry cultivars for286 strains of ice nucleation-active bacteria from 20 their efficacy in controlling anthracnose-crown rot. The

When 12 peach orce inle eon-act ere tete ed, all fungicides were applied weekly for 10 weeks at the followingapple and 12 peach orchards in Georgia were tested, all rates (g a.i./l water): benomyl, 1.3, 2.7, 3.6; captafol,produced fluorescent pigments and were negative for oxidase 19.2, 38.4, 76.8; and propiconazole, 0.3, 0.6, 1.2. After 4and arginine dihydrolase. Most strains resembled Pseudomonas fungicide applications, the plants wgre spray inoculatedsyringae pv. syringae in that they utilized erythritol, with a conidial suspension (1.5 X 10 conidia/ml) ofDL-lactate, and sucrose but did not cause pitting of poly- Colletotrichum fragariae. The mean disease severity ratingpectate media or soft rot of potato. Eighty-four percent (DSR) of each fungicide treatment was significantly lessproduced syringomycin. All except one strain produced a than that funtreate trol s (2.7). iPants tea whypersensitive reaction on tobacco. The strains were diverse than that for untreated controls (2.7). Plants treated withinpathogenicity acnd oirulenc n tobaco.ahe trains wereidiersen propiconazole had a significantly lower DSR (1.6) than thosein pathogenicity and virulence on green tomato fruit, green treated with either captafol (2.2) or benomyl (2.4). Plantsbean pods, and peach seedlings. Streptomycin resistance among inoculated with isolate MS-9 had a significantly higher DSR

strains was correlated with a history of streptomycin use in (2.2) than those inoculated with isolate CF-4 (1.8). Noorchards. Of 54 pesticides tested in vitro, dicofol, dinocap, significant effect of cultivars, fungicide rates, ormetalaxyl, and triforine were most active in inhibiting ice treatment eraction existed.

nucleation. treatment interaction existed.

EFFECT OF DISEASE RESISTANCE ON TOBACCO ETCH VIRUS EPIDEMICS SEEDLING DISEASES OF VEGETABLES ASSOCIATED WITHIN RELL PEPPER. R.G. Padgett, F.M. Nutter, Jr., and C.W. CONSERVATION TILLAGE AND FLUID DRILLING. Donald R. Sumner,Kuhn, Dept. Plant Pathology, Univ. of Georgia, Athens 30602. Suhas R. Ghate, and Sharad C. Phatak. Coastal Plain

Experiment Station, Tifton, GA 31793-0748.Incidence of TEV in bell pepper usually approaches 100% bytime of harvest in Northeast Georgia, resulting in signifi- Corn, okra, cucumber, cowpea, soybean, and tomato seedscant losses. Although pepper genotypes have been developed (intact or pre-germinated) were planted with fluid drilling

that differ in disease reaction to TEV, the effect of these into no-till or disked rye, on Bonifay sand and Tiftongenotypes on the rate of infection and yield has not been loamy sand, in March and April of 1985. Rows were drencheddetermined. Yolo Wonder B (YWB), Tambel 2 (TAM), and an with pencycuron plus metalaxyl, or nontreated, and irri-Asgrow line (susceptible, moderately resistant, and resis- gated immediately after planting. Plant stands weretant, respectively) were selected to quantify the effect of increased 65% and 20% with fungicides in the first andresistance on TEV epidemics. Disease incidence, assessed second plantings, respectively, but plant stands werevisually and by ELISA, was plotted with respect to time; the increased 49% without fungicides when planting in warmerinfection rate, relative area under the disease progress soils in April compared with March. In 1986, plantings ofcurve (RAUDPC), and yield recorded. Epidemics progressed cucumber, cowpea, and okra were made in no-till, disked, orfastest on YWB (RAUDPC=l.O) and slowest on Asgrow (RAUDPC=- plowed rye in April and May. Fungicides increased plant0.33). Tam was intermediate with a RAUDPC of 0.48. Asgrow stands 40% in Tifton loamy sand and 15% in Bonifay sand.and Tam increased yield by 32 and 12%, respectively, indi- There were no significant differences in plant stands amongcating that resistant genotypes offer a potential means of tillage treatments.managing TEV in Georgia.

SCLEROTIUM ROLFSII ON APPLE ROOTSTOCK: OVERWINTER SURVIVAL OFGROWTH AND SURVIVAL OF ARROWLEAF CLOVER INOCULATED WITH BEAN MYCELIUM AND HISTOLOGY OF INFECTION. S. F. Tomasino and K. E.YELLOW MOSAIC VIRUS AT DIFFERENT AGES. Indre J. Pemberton and Conway, Oklahoma State University, Stillwater, OK 74078-0285.G. R. Smith, Texas Agricultural Experiment Station, Drawer E,Overton, TX 75684. Domestic apple rootstock used for graft propagation of apple

and crabapple cultivars is an important host plant ofArrowleaf clover (Trifolium vesiculosum Savi.) plants were Sclerotium rolfsii (SR). A histological study of theinoculated with BYMV at five different ages and evaluated for infection process on apple seedlings and rootstocks inoculatedgrowth and survival. Eight plants each of arrowleaf breeding with sclerotia revealed aggregates of mycelium (infectionline 64 and variety 'Yuchi' were inoculated at 35, 63, 91, 119 cushions) in the crevices of bark that aid hyphal penetrationor 147 days. Uninoculated control plants were maintained into host tissue. Mycelium ramified within phloem and xylem,under identical conditions. All plants were clipped and dry resulting in vascular girdling 7 to 9 days after inoculation.matter measured four times at monthly intervals, beginning on SR mycelium was observed and isolated from tissue samples

Vol. 77, No. 4,1987 643

taken in early spring from dead rootstock killed at various alfalfa canopy with a Burkard 7-day spore trap and temperature,dates the previous year. This indicates that SR can relative humidity, leaf wetness and rainfall were monitored inoverwinter as mycelium. SR was readily isolated from trees the canopy using a datalogger and electronic sensors at onekilled late in the growing season while those killed from site in 1985. During the seven l-wk periods examined,early-season infections lacked active mycelium. quantities of L. briosiana ascospores and S. botryosum conidia

were positively correlated (P=0.23). When quantity of inoculumobtained for each fungus each week was related to environmintalconditions during the previous 7 days, spore density per m for

'TAM RIO GRANDE GOLD-SWEET' - A NEW MULTIPLE VIRUS- both fungi was correlated negatively with mean maximumRESISTANT, YELLOW WAX PEPPER CULTIVAR. B. Villalon, temperature (P<O.05) and mean rainfall (P<O.12), and positivelyTexas Agricultural Experiment Station, 2415 East (P<0.20) with mean leaf wetness duration. These possibleHighway 83, Weslaco, Texas. associations indicate the potential importance of environmental

factors in ambient inoculum density during epidemics of alfalfaThe Texas Agricultural Experiment Station at Weslaco leafspot.

has released a new multiple virus-resistant (MVR)

pepper cultivar. 'TAM Rio Grande Gold-Sweet' (TRGG)is a MVR, small-yellow wax, nonpungent, pickling-type pepper. This high yielding, conical, diamond YIELD RESPONSE OF ANNUAL CLOVERS TO MELOIDOGYNE INCOGNITAshaped, 'Caloro' type sets early concentrated fruit UNDER FIELD CONDITIONS. G. L. Windham and G. A. Pederson,on a compact plant with thick foliage. 'TRGG' USDA, ARS, Forage Research Unit, P. 0. Box 5367,possesses genetic resistance to tobacco etch virus Mississippi State, MS 39762(TEV), potato virus Y (PVY), pepper mottle virus(PeMV) and tobacco mosaic virus (TMV). The sweet, The effect of Meloidogyne incognita on 'Bigbee' berseemyellow fruit are well-suited for fresh market con- clover, 'Yuchi' arrowleaf clover, and 'Chief' and 'Tibbee'sumption in salads, or as a processed, pickled, crimson clovers was determined by comparing yields inwhole product. Extensive performance trials in infested and noninfested plots. M. incognita was increasedTexas and other areas indicated 'TRGG' has a wide in the nematode-infested plots by growing infectedrange of adaptability. 'Floridel' tomato prior to planting the clovers.

Uninoculated tomato plants were grown in check plots. Themean initial nematode populations at planting for Bigbee,Yuchi, Chief, and Tibbee were 1227, 940, 1188, and 832,

ASSOCIATION BETWEEN AMBIENT INOCULUM DENSITY OF TWO ALFALFA juveniles/500 cm3

of soil, respectively. Plots were 2.4 xLEAFSPOT PATHOGENS AND MICROENVIRONMENTAL FACTORS. K. Von 4.8 meters and bordered by fescue sod to minimize nematodeChong, C. Lee Campbell and E. Echandi. Dept. Plant Pathology, movement. Forage was harvested four times from the BigbeeNorth Carolina State University, Raleigh 27695. and Yuchi plot starting in February, 1986 and once from

the crimson clover plots in April. Yield losses for totalSpore density of Leptosphaerulina briosiana and Pleospora yields of Bigbee, Yuchi, and Chief were 11%, 3%, and 10%,herbarum (Stemphylium botryosum) was mFnitored in or above the respectively. Tibbee was unaffected by M. incognita.

644 PHYTOPATHOLOGY